Friday, July 18, 2014

Everybody
knows that sunlight makes plants grow. But did you know that solar
energy can help you “grow” healthier soil? If not, welcome to the
solar-powered world of soil solarization!

Solarization
is a safe, non-chemical, and effective method for controlling the host
of pests and diseases which might be lurking in your garden soil --
harmful bacteria, fungi, and nematodes, as well as insect eggs,
root-gnawing larvae, and weed seeds.

Of course, most of
your landscape gets along just fine without special intervention, but
for vegetable gardeners and folks with specialized garden beds, such as
dahlia collections or an annual cutting garden, going solar can help
prevent problems, while enhancing any site’s horticultural performance.

Solarization
is a creative spin on the greenhouse effect, which uses simple plastic
sheeting and the sun’s radiant energy to help sanitize the top six to
eight inches of garden soil. And although the process does require
setting aside a garden area for about two months during the summer, it
is far safer and less expensive than using toxic soil pesticides or
other fumigation methods.

Experienced gardeners know
that they should rotate their vegetable crops each year and select
disease-resistant varieties to control soil-borne diseases. However,
this is not always a practical option for some gardeners with limited
space, and after a while, any soil used and planted repeatedly with
similar crops will be still be infested with damaging populations of the
most persistent pathogens, like verticillium and fusarium wilt, as
well as parasitic nematodes, along with other weed and pest problems.

By
using solarization to dramatically elevate soil temperatures up to 140
degrees for a period of weeks, you can essentially bake those problems
away. Moreover, solarized soil is rapidly re-colonized by beneficial
bacteria and fungi, such as those which help fix nitrogen in the soil,
while yet other beneficial microorganisms will fill the void to help
fight off pathogens in the future. In short, your soil will be healthier
and better able to enhance plant growth and crop yields.

To
begin, select a garden bed or planting area at least 30 to 36-inches
wide, which is normally the most practical width for planting. Smaller
strips probably will not generate or retain enough heat to be effective.

Remove
all visible vegetation and other plant debris, and then cultivate the
soil to a depth of six inches or more. It is generally preferable to
use a rototiller to break up any clumps and provide a smooth, friable
medium. Keeping the texture of the soil smooth is essential to prevent
the formation of air pockets which will interfere with heat generation
and conduction. Also, carefully rake over the surface of the planting
area to ensure that it is completely free of stones or other coarse
materials which might tear or puncture the plastic sheeting.

During
cultivation, be sure to add any desired organic amendments such as
compost, or any fertilizer or lime, which might have been called for by a
soil test. If you are planning to use soaker hoses or drip irrigation,
you should put those elements in place now. Please note that after
solarization, you do not want to till or disturb the soil, as that will
only expose buried weed seeds. Finish by digging a trench approximately
six to eight inches deep and wide around the perimeter of your garden
bed.

Next, water the planting area thoroughly. Use a
sprinkler or soaker hose system and let it soak the prepared soil for
at least several hours, penetrating almost to a depth of one foot.
Every square inch of soil must be moistened for adequate heat
generation.

Afterwards, cover the area with a clear
plastic sheet made from UV-stabilized or resistant polyethylene or PVC.
Untreated plastic film will degrade in sunlight, and neither black nor
opaque plastic will generate sufficient heat.

Selecting
the proper thickness of plastic tarp is important. While very thin
film (.5-1 mil) is less expensive, it tends to rip very easily, and
would only be suitable for one use. Thicker plastic (4-6 mil) is
tougher and lasts longer, but does not allow as much more sunlight to
pass through. Instead, try to find a medium sheet (1-3 mils), and
stretch the plastic tight and smooth across the planting surface.

In
addition, for increased effectiveness, consider using a double-layer
of plastic with an insulating air space between the layers. You can
easily separate the two layers using empty aluminum cans. The extra
layer can increase soil temperatures by another six degrees, while also
retaining more heat on overcast days and at night.

After
getting your plastic firmly in place and tucked down into your trench,
backfill with soil to bury the ends of the sheet – and just wait for
the sun to do the rest. If your solarized bed is in an especially windy
location, you might want to place some bricks or rocks on top of the
trenched area as an additional anchor.

For the most
part, solarization should be undertaken anytime during the hottest,
brightest months, from June through August. It can be done earlier or
later, but additional time under wraps would be required, up to three
months. Traditional summertime treatment requires four to six weeks,
and as much as eight, if the skies were particularly cloudy, or if you
have been plagued with stubborn, noxious weeds for years.

After
solarizing, carefully remove and store the plastic for another use in a
subsequent year. You garden bed is now ready for planting. If you do
not plan to plant for several months, with a cool weather crop, for
example, be sure to cover the bed with a weed-free mulch.
Lastly,
remember that solarization only eliminates or reduces pest organisms
and weed seed from the top several inches of soil. Do not disturb your
sanitized soil any more than is necessary to slip in your new plants.

Home Composting Essentials

LEED Platinum Home Tour

Join me as I visit the first LEED Platinum residence in the Commonwealth of Virginia.

The Energerium

Explore an educational resource that explores the interconnectedness of people, land, and the energy that runs through all living systems.

Home Energy Audit

Here's a quick overview of home energy audits and learn about the small repairs and fixes that can add up to big savings on your energy bill.

Crystal City: Going Green

Visit Crystal City in Arlington, Virginia, where green practices at the Farmer's Market range from CSA support to transportation, energy efficiency, waste reduction and innovative composting programs.

Rooftop Retreat

With containers, favorite furnishings, and the right plants, you can turn your rooftop terrace or balcony into a lovely green oasis. Above, just a small corner of the GreenMan's rooftop overlooking Arlington, Virginia and Washington, D.C. Click on the image to learn more about creating a penthouse paradise in "High-Rise Horticulture" (July 20, 2009).

Butterfly Gardens

You can invite these winged jewels home to share with your family - and add color to your landscape. Click on the image above to read "Creating a Butterfly Garden" (Aug. 3, 2009).

About the GreenMan

I have been an environmental program director and educator for the past 25 years. I am also a writer, editor, columnist, and publisher, sometime producer, and off-and-on radio and cable television host.

The GreenMan? Beyond my educational background in Medieval Studies, and my personal interest in the image and myth of the "Green Man," I’ve taken on the term as a colorful bit of “branding” for my televised GreenMan Show and my long-running GreenMan newspaper column, which inspired many of the posts you find here.